1. Field of the Invention
The present invention relates to a nonvolatile semiconductor storage device and manufacturing method therefor.
2. Background Art
Since a NAND-type flash memory leaves bit line control to a selection transistor, it can be made smaller in cell area than a NOR-type flash or DRAM. Thus, NAND-type flash memories can be manufactured at a low cost.
However, as NAND-type flash memories are being miniaturized, the spacing between memory cells (the width of an STI) decreases with a decrease in size of memory cells. This produces the proximity effect in memory cells and causes interference between memory cells. Interference between memory cells acts to average the potentials of adjacent floating gate electrodes. Accordingly, a threshold difference (ΔVTH) narrows between a state wherein data is written and a state wherein data is erased, thus resulting in a data write failure.